1. Field of the Invention
The present invention relates to a scanning optical system.
2. Description of the Prior Art
In carrying out deflection scanning of a beam by rotating or rotationally oscillating the reflecting surface of a deflector according to the prior art, the beam incident upon the deflector is so directed as to enter it in the direction parallel to the reference deflection plane of deflector. For the purpose of this specification, the term "reference deflection plane of deflector" means such a plane which a normal of reflecting surface of the deflector describes when the deflector rotates.
On the other hand, it is known that a substantial reduction in size of the deflecting surface of deflector is allowed when the incident beam has a certain definite angle relative to the reference deflection plane of deflector. However, in this case, the surface which the deflected beam describes is not a plane surface but a conical one. This is disadvantageous when linear scanning is desired.